java线程状态和线程调度

旧城等待， 2022-08-31 09:46 251阅读 0赞

[java线程的创建和启动][java]

### 文章目录 ###

*  多线程
 *   *   *  线程的状态
         *  线程调度
         *   *   *  线程优先级
                 *  线程休眠
                 *  阻塞线程
                 *  线程礼让
                 *  线程调度练习

# 多线程 #

### 线程的状态 ###

![Java 线程状态、线程池状态\_shadow\_zed的博客-CSDN博客\_java 线程池的状态][Java _shadow_zed_-CSDN_java]

package Threads;
    
    public class MyThread5 implements Runnable { 
        @Override
        public void run() { 
            System.out.println("线程正在运行，处于运行状态");
            try { 
                System.out.println("线程开始休眠，处于阻塞状态");
                //线程休眠5S
                Thread.sleep(5000);
                System.out.println("线程休眠结束，阻塞状态结束，再次进入就绪状态");
            } catch (InterruptedException e) { 
                e.printStackTrace();
                System.out.println("线程中断");
            }
        }
    }

package Test;
    
    import Threads.MyThread5;
    
    //测试线程的状态
    public class MyThread5Test { 
        public static void main(String[] args) { 
            Runnable runnable = new MyThread5();
            Thread t = new Thread(runnable);
            System.out.println("线程处于创建状态");
            t.start();
            System.out.println("线程处于就绪状态");
        }
    }

### 线程调度 ###

##### 线程优先级 #####

由于线程之间的运行是通过抢占CPU的资源来进行的，线程调度指的是按照特定的机制为多个线程分配CPU的使用权。  
![请添加图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1NjcxNzMy_size_16_color_FFFFFF_t_70]

线程的优先级由1-10表示，1表示最低，10最高，默认的优先级是5。优先级高的线程获得CPU的资源概率比较大.

尝试更改线程的优先级:

package Threads;
    
    //创建线程类，实现Runnable接口
    public class MyThread2 implements Runnable { 
        @Override
        public void run() { 
            for (int i = 1; i <= 100; i++) { 
                System.out.println(Thread.currentThread().getName() + ":" + i);
            }
        }
    }

package Test;
    
    import Threads.MyThread2;
    
    //测试线程
    public class MyThread2Test { 
        public static void main(String[] args) { 
            //创建线程对象
            Runnable runnable = new MyThread2();
            Thread thread = new Thread(runnable, "mythread1");
            Thread thread1 = new Thread(runnable, "mythread2");
            //线程调度，设置线程优先级
    // thread1.setPriority(10);
    // thread.setPriority(1);
            thread1.setPriority(Thread.MAX_PRIORITY);
            thread.setPriority(Thread.MIN_PRIORITY);
            //启动线程
            thread.start();
            thread1.start();
        }
    }

##### 线程休眠 #####

线程调度的另一个方案是线程休眠。让线程展示睡眠指定的时长，线程会进入到阻塞状态，睡眠时间过后的线程会再进入可运行的状态。

方法是:

> public static void sleep(long millis)

millis是休眠时长，以毫秒为单位，调用sleep()方法需要处理InterruptedException异常。

package Threads;
    
    //模拟线程休眠的过程
    public class Wait { 
        public static void bySec(long s) { 
            for (int i = 1; i <= 5; i++) { 
                System.out.println(i+"秒");
                try { 
                    Thread.sleep(1000);
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
            }
        }
    
        public static void main(String[] args) { 
            System.out.println("线程开始休眠");
            Wait.bySec(5);
            System.out.println("线程结束休眠");
        }
    }

##### 阻塞线程 #####

*  join()方法  
    等待该线程终止，等待加入的其他线程结束后在继续执行本线程

package Threads;
    
    public class MyThread6 implements Runnable { 
        @Override
        public void run() { 
            for (int i = 1; i <= 30; i++) { 
                System.out.println(Thread.currentThread().getName() + ":" + i);
            }
        }
    }

package Test;
    
    
    import Threads.MyThread6;
    
    public class MyThread6Test { 
        public static void main(String[] args) { 
            //创建子线程对象t
            Runnable runnable = new MyThread6();
            Thread t = new Thread(runnable, "myThread");
            t.start();
            //主线程main做的事情
            for (int i = 1; i <= 20; i++) { 
                System.out.println(Thread.currentThread().getName() + ":" + i);
                //当i = 5的时候，强制把t线程加入执行
                //线程调度:join()--等待线程终止，等待t线程执行结束后，main主线程再继续执行
                if (i == 5) { 
                    try { 
                        t.join();
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            }
        }
    }

##### 线程礼让 #####

*  yield()方法

暂停当前线程，允许其他具有相同优先级的线程获得运行机会，该线程处于就绪状态，不会转为阻塞状态。这是线程之间的礼让问题，只是提供一种可能，但是不能保证一定会礼让成功。

package Threads;
    
    public class MyThread7 implements Runnable { 
        @Override
        public void run() { 
            for (int i = 0; i <= 4; i++) { 
                System.out.println(Thread.currentThread().getName() + ":" + i);
                if (i == 3) { 
                    Thread.yield();
                }
            }
        }
    }

package Test;
    
    
    import Threads.MyThread7;
    
    public class MyThread7Test { 
        public static void main(String[] args) { 
            Runnable runnable = new MyThread7();
            Thread t1 = new Thread(runnable, "线程A");
            Thread t2 = new Thread(runnable, "线程B");
            t1.start();
            t2.start();
        }
    }

##### 线程调度练习 #####

*  优先级问题

package Threads;
    
    public class MyThread8 implements Runnable { 
        @Override
        public void run() { 
    
        }
    }

package Test;
    
    import Threads.MyThread8;
    
    //获取和设置主线程和子线程的优先级
    public class MyThread8Test { 
        public static void main(String[] args) { 
            //主线程
            Thread mainThread = Thread.currentThread();
            //子线程
            Thread myThread = new Thread(new MyThread8());
            System.out.println("默认的优先级");
            System.out.println("主线程名:" + mainThread.getName() + "优先级:" + mainThread.getPriority());
            System.out.println("子线程名:" + myThread.getName() + "优先级:" + myThread.getPriority());
            System.out.println("修改优先级后");
            mainThread.setPriority(Thread.MAX_PRIORITY);
            myThread.setPriority(Thread.MIN_PRIORITY);
            System.out.println("主线程名:" + mainThread.getName() + "优先级:" + mainThread.getPriority());
            System.out.println("子线程名:" + myThread.getName() + "优先级:" + myThread.getPriority());
        }
    }

*  练习
    
    需求：某一个科室一天需看普通号20个，特需号10个，特需号的看病时间是普通号的2倍。开始时普通号和特需号并行叫号，叫到特需号的概率比普通号的高。当普通号叫完第10号时，要求先看完全部的特需号再看普通号。

package Threads;
    
    public class SpecialThread implements Runnable { 
        @Override
        public void run() { 
            for (int i = 1; i <= 10; i++) { 
                System.out.println("特需号:" + i + "号病人正在看病");
                //线程休眠来表示看病的过程
                try { 
                    Thread.sleep(1000);
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
            }
        }
    }

package Threads;
    
    //模拟医院看病
    public class CommonThread { 
        public static void main(String[] args) { 
            //当前线程--普通号
            //创建一个特需号的线程
            Thread special = new Thread(new SpecialThread());
            special.setPriority(Thread.MAX_PRIORITY);
            special.start();
            for (int i = 1; i <= 20; i++) { 
                System.out.println("普通号:" + i + "号病人在看病");
                try { 
                    Thread.sleep(500);
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
                if (i == 10) { 
                    try { 
                        special.join();
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            }
        }
    }

*  多线程数据共享问题

多个线程共享数据时，可能会引发数据的不安全问题。

package Threads;
    
    public class TicketThread implements Runnable { 
        private int ticket = 10;//记录车票总数
        private int num = 0;//记录用户抢到了第几张票
    
        //用户抢票
        @Override
        public void run() { 
            while (true) { 
                if (ticket <= 0) { 
                    break;
                }
                //有余票，则抢票
                //修改车票数:总票数在抢完票后减一张
                ticket--;
                //用户抢完票后，票数加一
                num++;
                //模拟网络延迟
                try { 
                    Thread.sleep(500);
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
                //显示出票反馈给用户
                System.out.println(Thread.currentThread().getName() + "抢到了第" + num + "张票,剩余" + ticket + "张票");
            }
        }
    }

package Test;
    
    import Threads.TicketThread;
    
    public class TicketThreadTest { 
        public static void main(String[] args) { 
            Runnable runnable = new TicketThread();
            Thread t1 = new Thread(runnable);
            Thread t2 = new Thread(runnable);
            Thread t3 = new Thread(runnable);
            System.out.println("各方开始抢票");
            t1.start();
            t2.start();
            t3.start();
        }
    }

[java线程同步][java 1]

[java]: https://blog.csdn.net/qq_45671732/article/details/118996491
[Java _shadow_zed_-CSDN_java]: /images/20220829/3f36699b96c04967aaed1a46c4dea2ad.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1NjcxNzMy_size_16_color_FFFFFF_t_70]: /images/20220829/008043d483434f4b8ca8ed9eb9813914.png
[java 1]: https://blog.csdn.net/qq_45671732/article/details/119139085